Intake type unloader for compressors and the like



April 22, 1952 w, DALRYMPLE 2,594,132

INTAKE TYPE UNLOADER FOR COMPRESSORS AND THE} LIKE Filed NOV. 2, 1945 3 Sheets-Sheet l INVENT OR. ZU/Y/fam Pfla/gmp/e BY 4 WA W ATTORNEYS April 22, 1952 w. P. DALRYMPLE 2,594,132

INTAKE TYPE UNLOADER FOR COMPRESSORS AND THE LIKE Filed NOV. 2, 1945 5 Sheets-Sheet 2 INVENTOR.

W/W/am DO/gm /e Ada [Aw Mi (lo/"MN ATTORNEYS April 22, 1952 w. P. DALRYMPLE 2,594,132

INTAKE TYPE UNLOADER FOR COMPRESSORS AND THE LIKE Filed Nov. 2, 1945 3 Sheets-Sheet 3 V 91 2 g a 525 if! 7 80 j :89 88 37B 60B 625 56B 52 e315 9 425 Q i \55 B 8 I} l '7 525 11 x 37 80 625 T539 88 V i 505 63 8 55B 92 42B INVENTOR. ZM/fidm Pp g f LJWQLWW ATTORNEYS Patented Apr. 22,

UNITED STATES .t ,7 W I5 132 iNTARE TYPERUNLOADERFOR- COMPRES- SOR 4ND THE LIKE RochesteryN. Y.,- assignor to: American Brake Shoe Company, Wilmington, sss retioaq w e,

A plication November 2, 1945, Sel No. 6233,228

7 Claims.

Ilihisz nv ntion re tes qau omat lm q @XS andpaitioula y to-what otpown; a 26 type of unloaders for use in connection with air compressors and th e qlilne U l ad s the a oresoi tohata or, re. o trol edty thepre ureyo a ps hezpross ie tank so that the intake; of; the compressor is lo e h n-- h t n p ssu e; e qho .zersor met lim m; h b ors onart r s mply.

immnmfld a opthox nk w l at th some me removinao a uo oethemed on the m: P ston. n H-w en thetank ros oroi b en re uoedginea; re ermin d amo nthos oi. air-- he e ro ethe;intake of thooommessori opened and the compression of air is again reme r 1:71;. V ous o sy a e beo aem loyede o @195 the. -i ake of om e ors on.-,-un adin t u z poses, and such means have usually bee o m 0. c m licat d n t n..: o--;a ood al mechan m o era ng-un erj essi ra m the Q 1PI6 QI h -:ofii iono o th -o o o ed o d a: see to zu onh e e of so rt lt o i o ist otio o e-inter,

r t os oi th aorta h t ot ere en to s. t i f l rthogoon ruot onro rmt et pe' unloaders loy ,completely eliminating the use of piston and needle yalvese, r t io i nta e-:tyne pimlo or .mpl r n Pist n. an n dl a vesbor meoe sa r b en m t -to ef ve op at o -o er,- on y-.-a rela: tively. rrow r o r sure varia i ns; ince. a re ed p n by -mross re-hosbeen l t yp i te s :I is: th o .uanothoe ooi'e t, the 1 so ri f en onet ma eria l in:

rea e th e a n e su oreyoriations ;.1ovo w ch e fioot v Qn r tionv t uto a oessu e;

the foregoing is. to provide a greatly inereased;

tes lieei wh 'ch t elrni ie; wo ki ee-vp o so e ma act 1 a d zmot rs fioall v t o io d :suoh

area by a diaphragm of relatively large diamtoo fii il fia i iie' att i mom; o tho o e r: mi d: Pressu e n. f hQjt' Pkii .111 16 any or ppreoir ti l m h mo e da gerou e therwi o n:

de'iible". Accordingly it is still a further object i 'h r t o nza l id t-rinstanrir/ i n en ion-Jo h f ord: an zunloader @thams hi hly so s iro:andioap b ehof;instantaneous resp nse-topred t m n dtank press r a: 33 .118 ancillarytq the foregoin are to providesa pair o i raems,one-responsive tfl rthe pres-V s re ith tan -and; a apted to open a pil valve; to a mainworking-chamber having; a relr atively, l, reer;d h aem :whiohyby' r ason :of i larg Work ne i-a earresponds .lteadilmto'ismall pressure variations to close the air intake of the mD QSWI-"J 1 :g i, ":S', Ii;

Yet another object of; this inventionv i s,-.- to; af: ford a diaphragm actuatedg-automatic'qpressure 1 unloader wherein-the sequence; of V Operations-is sotimedaand; arranged asrto afford greatly increased efiiciency and speed --in;unloading 0b jeqts vrelating.tothe vforegoina-zarevto; ilvrevent. the exhaust or wasteof-air-to atmospherefrom ho Wo kin ;.cham.ber-. o the; di p ragm during the time that airisbeing; admittedptheneto :iqrythe, purpose of operating;thev mainzdiahmsmand: th as oo at d nloa ina lre-a zo t lano er-object istil iplfflvidfian improved d aph m; p rated. unloader; 'whiohwis; so; a1: ranged-that the fiexible diaphragms may easily be @191 jwhe noc ssary 5;; 1;; l llf...

applyingthat principle-w Othen'embodiments of the inventionaembodying the same or: equivalent: principle-may be used and structuralchanges may-oibeamade: as vdesired by :those-skillednin other artwithout' departing :fronrthe presentdnvent-ion and-the-puryiewof the appended claims.

In,:the drawingsgwi F ."szu 01:? ii 1 1.; -2-= Fig. 1 is a partially.- di grammatic' elevational; View Ofxra-compressorisystemj includingvza :tank and; compressor shownrpartiall-y-in; sectionezandf equipped w-ith the automatic intake unloader of the pr sen nv ti nr; 4;":11-1-6 1": "525-1 :.Frig.: -2a-is :an enlarged; cross-sectional the unloader in its open position;

Last, 1

view of Fig. 3 is a top plan view of the apparatus;

Fig. 4 is a cross sectional view of the apparatus in its unloading position wherein the pilot valve is open and the main unloading valve is closed;

Fig. 5 is a similar cross sectional view showing the apparatus at substantially the end of an unloading cycle when the pressure controlled pilot valve has been closed and the main unloading valve is about to start from its closed position to its open position;

Fig. 6 is an enlarged sectional view of the pilot valve and diaphragm mechanism of another embodiment of the invention;

Fig. 7 is a similar cross sectional view showing the parts in an intermediate relationship assumed during the opening and closing movements of the pilot valve; and

Fig. 8 shows the pilot valve in its fully open position.

For the purpose of disclosure the invention has been herein illustrated in Figs. 1 to 5 as embodied in an unloader l0 and is shown in Fig. 1 in position on the intake ll of a compressor C. The compressor 0 is shown as a part of a compressor system which includes a pressure tank T that is charged by the compressor through a discharge line I IA. The compressor C has a piston l2 that is reciprocable in a cylinder l3 by conventional means including a crank shaft [4 and a piston rod l5, and conventional inlet and outlet valves l'! and I8 are afforded for controlling the passage of air from the inlet II and through the cylinder [3 to the tank T. r

The unloader I0 is in the nature of an automatic valve, as will hereinafter be fully described, and may be closed so as to close the intake 1 I of the compressor'or may be opened so as to permit normal flow of air into the intake l I of the compressor. Such operation of the unloader is under control of the pressure in the tank T, and forthis purpose, a control pipe or connection is extended from the tank to the unloader I0.

The'specific construction of the unloader of the present invention is disclosed in Figs. 2 to 5 of the drawings, wherein it will be observed that the unloader has a main body in the nature of an L-valve body that aifords tubular arms 25A and 25B disposed at right angles to each other and having threaded axial openings 26A and 26B formed therein so as to open into the hollow interior of the valve body 25. Inwardly of the opening 26B, the valve body 25 has a sleeve-like extension 21 that defines a valve orifice 28 having a flat valve seat 29 surrounding the upper end of the orifice 28, and this valve orifice 28 opens into a chamber 30 formed within the valve body 25 so as to'communicate with the opening 26A. The openings 26A and 26B are disposed at right angles to each other so that fluids such as air may pass through the valve body, and such flow of fluid through the valve body is controlled by a disc-like valve member 3| disposed within the chamber '30 and having a resilient surface arranged to seat against the valve seat 29 so as to close the valve opening 28. The valve member 3| is carried on a valve stem 32 that is reciprocable in a bearing sleeve 33 so that the valve member 3| may be moved from the closed position of Fig. 4 to the open position of Fig. 2. 1

The bearing sleeve 33 is in the present case formed in an axial relation on a spring supporting plate 34 that is carried on an upwardly facing shoulder 35 formed at the lower end of an axial opening 36, the opening 36 being formed in the valve body in alignment with the opening 26B and the valve opening 28. The upper end of the valve stem 32 extends beyond the bearing sleeve 33 and means including a spring 31 are associated with the extended upper end of the valve stem 32 for controlling the position of the valve 3i.

In accordance with the present invention, the valve operating means are afforded by a flexible main diaphragm 40 that is rested about its outer edges upon a mounting flange 4| that is extended outwardly about the upper end of the opening 33. The peripheral edge of the diaphragm is clamped against the flange 4! by a mounting plate 42 the edge flange 42A of which bears against the border portion of the diaphragm 43. The mounting plate 42 is held in place by a plurality of cap screws 43, Fig. 3, so that the mounting plate 42 may be readily removed for inspection or replacement of the diaphragm 40. The valve body 25 is tapered downwardly as at 44 about th border portion of the opening 36 so that the diaphragm 40 may be bent downwardly to the position shown in Fig. 4, while the lower surface of the mounting plate 42 is recessed upwardly as at 45 so as to define a pressure chamber 46, Fig. 4, and the diaphragm 40 may be bent upwardly against the surface'45 as viewed in Fig. 2 in order to permit opening movement of the valve 3 I. Such upward flexing of the diaphragm 40 is attained by the coiled spring 31 which bears at its lower end on the plate 34 and at its upper end on a disc 41 that bears against the lower face of the diaphragm 40. The disc 41 has a downwardly facing central hub 41A formed thereon that embraces a tapered upper end 32A on the valve stem 32, thereby to aid in locating these two parts with respect to each other, and the disc 41 and the stem 32 are caused to move as a unit by welding the hub 41A to the surface 32A.

The mounting plate 42 has a pressur inlet port 48 formed centrally thereof so that the pressure fluid may be supplied to the pressure cham ber 46 for the purpose of forcing the diaphragm D from its upwardly extended position of Fig. 2 to the downwardly extended position of Fig. 4, thereby to close the valve 3|, and when the valve 3| is to be closed for the purpose of unloading the compressor, the necessary pressure fluid is admitted to the pressure chamber 46 through the valve opening 48 under the control of valve means that are associated with the valve opening 43.

Such valve means that are associated with the port or valve opening 48 are in the nature of a 55 pilot valve and are arranged for operation by diaphragm means that are mounted upon the upper face of the mounting plate 42. Thus the mounting plate 42 has an annular recess 50 formed in its upper surface so as to form an inner to rim 5| about the valve opening 48, and the annular recess 58 also afiords an upstanding outer rim 52 upon which a control diaphragm 55 of flexible construction is mounted. The inner rim 5| has a flat upper surface that aifords a. valve seat 55 against which a resilient valve' member 51 may be seated, and the valve member 51 is carried on the lower face of the control diaphragm 55 in a manner that will be described in detail hereinafter.

The control diaphragm 55 is clamped in position about its outer edge by an inverted cuplike spring housing 58 that is flanged at-58A at its lower'end, and clamping screws 59 are ex-' 5 the-mounting" plate 42. tionsofthec'ontrol diaphragm 55 aresecured in position about the top of the rim 52 so that the annulafrecess' 50 constitutes a control chamber. The-control chamber 50 hasa bore 62 extended radially-therefrom and the outer end of thebore 82 -hasan' enlarged tapped portion 53 to which the control pipe is connected. The pressure from'-- the tank T is thus applied to the control chamber so as to tend to raise the diaphragm to its upwardly bent position of Fig. 4, but this isresisted'by an adjustable control spring 55 that housed within the spring housing 58. The lower end of the spring rests upon an annular guide or pressure plate 65 that is slidable verticallywithin a cylindrical guide surface 61, and thelower face of the plate 65 rests uponthe uppeffa'ceof the control diaphragm 55. The plate 664s "utilized'lnthe present instance in affording a -niountin'g-forthe valve 51 on the diaphragm 55 and'for'this" purpose a mounting bolt 68 is passed through the valve 51 so that the head of the bolt is exposed on the lower face of the valve, the location being such that the head of the bolt 58 may freely enter the valve opening 48. The bolt extends through the diaphragm 55 and the plate 66 and a nut 68A is provided on the upper end of-the bolt 68 so that the valve member 51 mayreadily be replaced when this is desirable.

At'itsupperend the spring 65 has a pressure plate 10' rested thereon and the tension or forc of the spring 55 may be adjusted by an adjusting screw II that is threaded downwardly through the upper end of the spring housing 58 so as to bear upon the pressure plate 10. The adjusting screw may be held in its adjusted position by a cap likelock nutlZ that embraces the upper end of the screw so that the lock nut may be tightened downwardly against a shoulder '13 on the spring housing. 7

The spring 65 is adjusted so that when the desiredmaximum pressure is attained in the tank T," the pressure'applied to the lower face of the control diaphragm 55 will be efiective to force thedi'aphragm 55 toward its upwardly bent position of 'Figfll; and when this occurs, the valve 51 is lifted from its valve seat 56 so that air pressure' fronithetank T may pass through the chamber- 50 and the valve opening 48' and into the main pressure-orworkingchamber 46. Thus the valve '5l a'cts as a pilot valve that under the circumstancesjust described permits-flower pressurefluld int'o the main working chamber 48, and the-diaphragm 40, being of relatively large diameter immediately flexes in a downward direction to the-position shown in Fig. 4, and this causes the-valve 31 to be moved to its closed position wherein the intake ll of the compressor C is closed. This of course serves to unload the compressor Cland since no further air is supplied to the" cylinder l3 of the compressonthere is no further increase of pressure within the tank T.

When the control diaphragm 55 is in its upper position, the effective area thereof is somewhat greate'rthan it'was prior to the opening of the valve'51,' for the lower face 'of the valve 51' now is exposed: to the pressure within thecontrolj chamber 50, and hence the diaphragm 55 will remain in'itsupper position of Fig. 4 until such time as-the pressure within the tank T has been reduced by'normal use or leakage to a value that r is somewhat'below the value at which the valve aree'ttecuver onthe dlap'hra'gm 55in the closed Thus the border por and open positions thereof; When the pressure in the tank T reaches" such a value that the" valve 51 returns to its closed position, the'supply or pressure fluid to the working chamber 45 is cutofi, and the diaphragm 40 starts to return to its upper position of Fig. 1. In order-that such return movement may take place, the air within the working chamber 46 must be dissipated, and in the'form of the invention illustrated in 1 to 5, this dissipating action is caused by a relaevery small relief port 15 that is formed asa'n axiaiboreina mg 16 that is screwed downwardly through the plate 42 so that the relief port 15 communicateswith the working chamber 46. The" size of the relief port 15 is relatively small so that during the period when the pilot valve 5 1 is" opened, the loss of pressure fluid-through the port 15 is negligible; and with the'relief port 15 so proportioned, the pressure'within the working" chamber 46 is dissipated quite rapidly after closure" to build up the pressure in the tank T toward the predetermined maximum value.

In some instances it may be desirable to avoidcontinuous venting of air from the working cham;

ber' 46 during the unloading periods, and inaccordance with the present invention this venting with the consequent waste of pressure fluid-may" be avoided throughthe elimination of the vent" i5 and through 'the'provision of a vent valve that is opened and closed as' an incident to theopera tion of the pilot valve. Such an embodiment of the invention is illustrated inFigs. 6, 7 and 8' of the drawings wherein the mounting plate that afiords the main pressure or working chamber of the unloader is fragmentally illustrated at 4213, and therelated or similar parts of the mechanism" are identified by similar reference characters with the s'ufiix B. Thus the mounting plate 423 has a centrally located valve opening 48B that terminates in an upstanding rim that afiords a' valve seat 5613 and this valve seat 56B is adaptedto be engaged by an annular valve member 5113 that is operated in accordance with the pressure in the tank T by a control diaphragm 55B, The

plate 423 has an outwardly" and upwardly extending annular portion that terminates in a flange or rim 52B upon which the border portion of the control diaphragm 55B is seated, and the border portion of the diaphragm 55B is held in place by the flanged lower end of a spring housing 58B of substantially the same character as that shown in Figs. 1 to 5. The'sloping annular" portion Bil serves to afiord an annular control chamber 503 disposed about the valve seat 563,

and a passage 623 with an enlarged screw threaded outer end 633 serves to enable the pres; 7 sure connection 20 to' be extended and connected to the control chamber 50B. The diaphragm 55B is normally pressed downwardly by a control spring 65B that is adjustable at its upper end in the same manner as shown in Fig. 2, and the pressure of the spring 55B is applied to the'diaphragm 5513 by a pressure plate 553. The pressure plate B6B differs considerably from that shown in the other' embodiment of the invention, in'that an upstanding annular wall 82 is pldvided'centrally of the plate aild'thls unfill- 7 lar wall 82 is closed at its upper end by a top wall 83. The wall 82 and the wall 83 serve to afford an inverted cup-shaped member that opens downwardly, and the internal surface of the annular wall 82 is screw threaded so as to receive a clamping sleeve 85 whereby a fiat bearing plate 86 is secured against the lower surface of the wall 83. The clamping sleeve 85 extends through a central Opening in the diaphragm 55B, and a lower clamping plate 81 is threaded onto the sleeve 85 so as to clamp the inner border portion of the diaphragm 55B against the lower surface of the plate 663. Thus the sleeve 85 moves up and down with the diaphragm 55B as it is flexed, and the sleeve 85 serves as a part of the mounting for the pilot valve 57B. Thus the pilot valve 513 has a flange 88 at its upper edge and this flange is disposed within the sleeve 85 and above an inturned annular flange 89 formed on the lower end of the sleeve 85. The pilot valve 573 is normally urged downwardly with respect to the sleeve 85 by a resilient means housed within the sleeve 85 and such means as herein shown are in the form of an expansive rubber sleeve 98 that bears at its upper end against the plate 86 and at its lower end against the upper face of the valve 513. Thus the valve 57B may be moved upwardly or downwardly with relation to the sleeve 85 and this capability is utilized in affording a vent valve means that is opened and closed in timed relation to the movements of the control diaphragm 553. To this end, the pilot valve 51B has a vent opening 9| formed axially therein and this vent opening terminates in a conical valve seat 92 disposed at the lower end of the vent opening. The valve seat 92 is adapted for cooperation with a complemental valve head 94 that is of conical form, and this valve head is formed at the lower end of a valve stem 95. This valve stem extends upwardly and through the horizontal wall 83 of the pressure plate 65B; At its screw threaded upper end, the valve stem 95 has a nut 93 threaded thereon so as to engage the upper surface of the wall 83, and thus the spacing of the valve head 94 with respect to the plate 83 may be adjustably determined. This adjusted relationship of the valve head 94 is such that when the resilient member 90 causes the valve member 51B to be moved to its most downward position, with the flange 88 in engagement with the flange 89, the valve seat 92 will he engaged with the valve head 94, thereby to close the vent opening 9|. When however the diaphragm 55B is forced downwardly to the position shown in Fig, 7, the lower face of the pilot valve 51B engages the seat 56B, and this of course shuts off the flow of pressure fluid from the control chamber 50B through the valve opening 48B. The continued downward movement of the diaphragm 55B thereafter serves merely to shift the valve head 94 downwardly with respect to the valve member 513 and the seat 92, thus to move the valve head 94 to the open relationship shown in Fig. 6. When this occurs, the pressure in the working chamber 468 is vented about the valve head 94 and through the vent opening 9 I.

When the pressure in the tank T again approaches the maximum value, the initial upward movement of the diaphragm 55B serves to move the valve head 94 upwardly from the open position shown in Fig. 6 to the closed position shown in Fig. '7, and this closed relationship of the valve head 94 is maintained as the upward movement of the diaphragm 55B is continued. Thus the vent opening BI is maintained closed during the time when the pressure fluid is applied through the valve opening 483 to the working chamber 463. As the pilot valve 51B is moved from its open position of Fig. 3 toward the closed position of Fig. 7, the closed relationship of the vent port 9| is also maintained, and it is only after the pilot' valve 513 has been closed that the vent port 9! is opened. Thus the arrangement provided in the embodiment of the invention shown in Figs. 6 to 8 conserves pressure fluid and insures efficient and effective operation of the unloader.

From the foregoing description it will be apparent that the present invention enables intake type unloaders to be embodied in a simple and effective structure wherein the parts may readily be assembled or disassembled for inspection or replacement. Moreover, this invention enables the valve operating movements to be attained through the use of diaphragms, thereby eliminating the use of pistons which have heretofore been found to be costly and otherwise objectionable. It will also be apparent that under the present invention, the pressure fluid may be conserved through the provision of a pilot valve and a vent valve that are operated in timed and interrelated relationship by the control diaphragm of the unloader.

Thus, while I have illustrated and described the preferred embodiments of my invention, it is to be understood that these are capable of variation and modification and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims:

Iclaim:

1. In an intake type unloader for compressors and the like, a valve body having a passage therethrough and affording a main valve opening defined in said passage, a valve member for cooperation with said main valve opening and mounted for movement between open and closed positions relative to said main valve opening, a main diaphragm operatively associated with said valve member for imparting valve closing movement thereto, means cooperating with said main diaphragm to afford a main pressure chamber having a pressure inlet opening, a pilot valve for said inlet opening, a control diaphragm operatively associated with said pilot valve for operating the same, means yieldingly urging said pilot valve toward closed position, means cooperating with said control diaphragm to afford a control chamber that communicates with said main chamber whensaid pilot valve is open, means for supplying control pressure to said control chamber, means affording a vent opening for venting pressure fluid from said main chamber, a vent valve for said vent opening, and means operable by said control diaphragm to open said vent valve when said pilot valve is closed, and close said vent valve when said pilot valve is open.

' 2. In an intake type unloader for compressors and the like, a valve body having a valve chamber and passage therethrough and. affording a main valve opening defined within said chamber, a valve member for cooperation with said main valve opening and mounted for reciprocating movement between open and closed positions relative to said main valve opening, a main diaphragm mounted exteriorly of said body in a plane at right angles to the reciprocating path of said main valve member and operatively associ: ated with said valve member for imparting valve closing movement thereto, a mounting plate fixed 9 on said body and'cooperatin'g with said main diaphragm to afford a main pressure chamber having a pressure inlet opening, a pilot valvefor said inlet opening, acontrol diaphragm operatively mounted on said mounting plate and associated with said pilot valve ior operating the same,

means carried on saidmountingplate and yieldingly urging said pilot'valvetoward closed position, said mounting plate being formed-to cooperate with said control diaphragm to afford a venting pressure fluid from said main chamber,

a vent valve for said vent opening, and means operable by said control diaphragm to open said vent valve when said pilot valve is closed, and close said vent valve when said pilot valve is open.

3. In an intake type unloader for compressors and the like, a valve body having a valve chamber and passage therethrough and affording a main valve opening defined within said chamber, a valve member for cooperation with said main valve opening and mounted for reciprocating movement between open and closed positions relative to said main valve opening, a main diaphragm mounted exteriorly of said body in a plane at right angles to the reciprocating path of said main valve member and operatively associated with said valve member for imparting valve closing movement thereto, a mounting plate fixed on said body and cooperating with said main diaphragm to afford a main pressure chamber having a pressure inlet opening, a pilot valve for said inlet opening, a control diaphragm operatively mounted on said mounting plate and associated with said pilot valve for operating the same, means carried on said mounting plate and yieldingly urging said pilot valve toward closed position, said mounting plate being formed to cooperate with said control diaphragm to afford a control chamber that communicates with said main chamber when said pilot valve is open, means for supplying control pressure to said control chamber, said pilot valve having a vent opening formed axially therethrough, and means operated by said control diaphragm to open said vent opening when said pilot valve is closed and to close said vent when said pilot valve is open.

4. In an intake type unloader for compressors and the like, a valve body having a passage therethrough and affording a main valve opening defined in said passage, a valve member for cooperation with said main valve opening and mounted for movement between open and closed positions relative to said main valve opening, a main pressure fluid operated means operatively associated with said valve member for imparting valve closing movement thereto, a pilot valve for controlling the supply of pressure fluid to said main pressure fluid operated means, a second pressure fluid operated means operatively associated with said pilot valve for operating the same, means yieldingly urging said pilot valve toward closed position, means for supplying control pressure to said second fluid pressure operated means, said pilot valve having an axial opening therethrough to afford a vent opening for venting pressure fluid from said main pressure fluid operated means, a vent valve for said vent opening, and means mounted on and operable by said second pressure fluid operated means to open said vent valve when said pilot War 10 a valve is closed, and close said vent valve when said pilot valve is open.

5. In an intake type unloader for compressors and the like, a valve body having a passage therethrough and'afio'rding a main valve opening defined in said passage, a valve member for cooperation With said main valve opening and mounted for movement between open and closed positions relative to said main valve opening, a main pressure fluid operated means operatively associated with said valve member for imparting valve closing movement thereto, a pilotvalve for controlling the supply of pressure fluid to said main pressure fluid operated means, a second pressure fluid operated means operatively associated with said pilot valve for operating the same, means yieldingly urging said pilot valve toward closed position, means for supplying control pressure to said second fluid pressure operated means, means affording a vent opening for venting pressure fluid from said main pressure fluid operated means, a vent valve element for said vent opening, means afiording a valve seat element about said vent opening, and means supporting said elements in fixed and relatively movable positions respectively on said second pressure fluid operated means so that said second pressure fluid operated means is operable to open said vent valve when said pilot valve is closed, and is operable to close said vent valve when said pilot valve is open.

6. In an intake type unloader for compressors and the like, a valve body having a passage therethrough and affording a main valve opening defined in said passage, a valve member for cooperation with said main valve opening and mounted for movement between open and closed positions relative to said main valve opening, a main pressure fluid operated means operatively associated with said valve member for imparting valve closing movement thereto, a pilot valve for controlling the supply of pressure fluid to said main pressure fluid operated means, a second pressure fluid operated means operatively associated with said pilot valve for operating the same, means yieldingly urging said pilot valve toward closed position, means for supplying control pressure to said second pressure operated means, means affording a vent opening for venting pressure fluid from said main pressure fluid operated means, a vent valve for said vent opening, and means operable by said second pressure fluid operated means to open said vent valve when said pilot valve is closed, and close said vent valve when said pilot valve is open.

7. In an intake type unloader for compressors and the like, a housing, a wall extending across said housing and having an opening through the central portion thereof to afford a valve port, a flexible diaphragm mounted in said housing and extending thereacross on one side of said wall, means for feeding Working fluid through said housing on the opposite side of said diaphragm from said wall, said means including a valve seat in said housing, and a valve member reciprocably mounted in said housing for movement between open and closed positions relative to said valve seat, a retaining member mounted in said housing on said opposite side of said diaphragm from said wall, a spring mounted on said valve between said retaining member and said diaphragm yieldingly maintaining said valve in abutting engagement with said diaphragm and urging said valve toward said open position, and means mounted on the 11 opposite side of said wall from said diaphragm and in communication with said port for selectively feeding working fluid through said port against said diaphragm to flex said diaphragm toward said valve seat and thereby move said valve member into closed position against the urging of said spring.

WILLIAM P. DALRYMPLE.

REFERENCES CITED Number 12 UNITED STATES PATENTS Name Date Boekel June 28, 1904 Anderson Oct. 17, 1905 Serrell Mar. 27, 1906 Williams Jan. 21, 1913 McManamy Oct. 12, 1915 Raymond Jan. 3, 1922 Raymond Sept. 30, 1924 Otto May 25, 1926 FOREIGN PATENTS Country Date Number Great Britain June 12, 1913 

